Various types of illumination structures are known. In general, as used herein, an illumination structure is a structure that emits light. Such illumination structures may be desired for various applications, from decorative lighting of a home or business (e.g., rope lights, etc.) to decorative lighting within small electronic devices, such as laptop computers or mobile telephones, etc. For a given application, a particular shape of the illumination structure may be desired. For instance, a shape that fits within a given electronic device may be desired. Further, it may be desirable for the illumination structure to emit light substantially evenly throughout. Many such applications in which lighting is provided primarily for aesthetic purposes are referred to as “fun light applications.”
A traditional illumination structure that designers have used for creating light designs for applications has included a light guide and one or more light sources. The light source generates the light and the light output by such light source is carried through the light guide. The light guide emits at least a portion of the light that it carries (e.g., the light guide glows). Common light sources that are used with such a light guide are Light Emitting Diodes (LEDs). FIG. 1 shows an exemplary illumination structure used in prior designs. The exemplary illumination structure includes a light guide 120 and LEDs 110. Light guide 120 is a plastic part with microstructures underneath to extract light from LEDs 110, and thus light guide 120 is a rigid part. LEDs 110 are attached at various locations on light guide 120 as a source of light. Unfortunately, applications of this type of illumination structure have been limited. The rigidity and inflexibility of the light guide 120 results in difficulty for designers in creating certain fashionable shapes that may be desired for a given application. Also, the basic structure of the light guide 120 results in an uneven distribution of the brightness of the light emitted by the light guide because of hot spots near the light sources and because of light leakage at the bends or curves of light guide 120. Also, an undesirably large number of light sources (e.g., LEDs 110) may be required to compensate for the poor light coupling (which may be referred to as “optical coupling”) of LEDs 110 to light guide 120 and light leakage from the curved portions of light guide 120.
Flexible light guides (which may be referred to as “light strips”) provide an alternative to the above-mentioned rigid light guide 120. Flexible light guides are available for carrying light from one or more light sources and emitting at least a portion of such light along the length of the guides. Because of their flexibility, such flexible light guides afford greater versatility to designers in creating illumination structures for various applications. The flexible light guides provide a significant improvement over the above-mentioned rigid light guide 120 in the evenness and brightness of the light emitted throughout the entire length of the flexible light guide, as well as greater flexibility. An example of a known flexible light guide is one composed of an outer Teflon clad surrounding an inner elastomer core. Such a flexible light guide is able to bend with a curvature of ten millimeters in diameter while retaining more than 80% of its illuminance. FIG. 2 shows an example of such a flexible light guide 220 to which a light source (e.g., LED) 210 is coupled. A typical method of coupling flexible light guide 220 to LED 210 involves use of a heat-shrink tube 230. For instance, LED 210 and light guide 220 are positioned as desired relative to each other within a tube 230 that has a sufficiently large diameter to encompass LED 210 and light guide 220. Heat is then applied to tube 230 to shrink such tube 230 (e.g., reduce the tube's diameter), thereby causing the heat-shrink tube 230 to engage the light guide 220 and LED 210 to hold those components in place relative to each other. For this type of illumination structure, LED 210 is a through-hole type LED, and an end of flexible light guide 230 is placed in contact with LED 210 such that light generated by LED 210 is directed through light guide 230.
Unfortunately, the method of using heat-shrink tube 230 as a means of attaching flexible light guide 220 to LED 210 has several disadvantages that are undesirable for certain lighting applications. The use of heat-shrink tube 230 results in poor light coupling (or optical coupling) between the optical center of through-holed LED 210 and flexible light guide 220. The efficiency of the light coupling is further reduced because the heat-shrink tube 230 is not a good reflector, resulting in a loss of light through absorption by the heat-shrink tube 230. Because through-holed LEDs are required in this illumination structure (because of the use of the heat-shrink tube 230 to couple LED 220 to flexible light guide 220), application of this illumination structure to miniature products is limited. Moreover, the overall design using a heat-shrink tube 230 for coupling flexible light guide 220 with LED 210 has not proven to be a robust design, and can fail as a result of mechanical or thermal shock.